Harmonic eliminator



P. W. BLYE HARMONIC ELIMINATOR Filed Nov. 21. 1927 Aug; 12', 1930.

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IN VEN TOR.

ATTORNEY Patented Aug. 12, 1930 UNITED STATES PATENT OFFICE PAUL W. BLYE, OF RUTHERFORD, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK HABMONIC ELIMINATOR Application filed November 21, 1927.

vention relates to arrangements for eliminating and substantially suppressing harmonics introduced by alternating current rectifying equipment which may, for example, be of the mercury arc type.

In systems for rectifying polyphase alternating current, a plurality of harmonic frequencies of the current supplied to the rectifier are. usually produced which may, and frequently do, interfere with the quality of speech transmitted over an exposed telephone circuit. It has been found that only certain of the harmonics of the frequency of the current supplied to the rectifier are produced thereby and are present in its output. These harmonics, upon analysis, have been found to be a plurality of successive harmonics, all harmonics of a predetermined harmonic of the current supplied to the rectifier. Any system for the suppression of superimposed currents, which includes numerous elements, involves considerable expense, and moreover, may introduce a complex problem involving the mutual reaction of these elements.

The inductive interference in telephone systems apparently results from alternating components of currents and voltage impressed upon the direct current circuits which are furnished with power from rectifiers which are frequently of the n'iercury arc type. The noise problems arising in the telephone circuits and in the telephone plants are becoming more serious as the use of the rectifiers, above mentioned, increases. This invention is intended to provide arrangements or reducing and substantially suppressing the causes of noise in the telephone circuits and plants.

One of the olnects of this invention is to provide means for reducing the variations in current or voltage superimposed upon the output of a polyphase rectifier, which variations may cause interference in exposed telephone circuits or the like.

It is another object of this invention to provide in a system employing a rectifier for Serial No. 234,855.

rectifying polyphase currents, a rotary converter associated with a source of alternating current having its direct current terminals operating in parallel with the output of the rectifier and one or more anti-resonant circuits in order that the harmonics introduced by the rectifier may become substantially suppressed thereby.

It is a further object of this invention to provide a so-called floating battery between the rectifier of alternating current and a power circuit over which the r ctified current may be transmitted. and one or more parallel resonant circuits so that the battery may act not only to transmit current over the power circuit during conditions of overload but also in conjunction with said parallel resonant circuits to suppress harmonic components produced by the rectifier and such other alternating currents as may become superimposed upon the power system.

Whilethis invention will be pointed out with particularity in the appended claims, the invention itself, both as to its further objects and features, will be better understood from the detailed description hereinafter following, when read in connection with the accompanying drawing, in which Figure 1 represents one embodiment of the invention, in which a rotary converter is shown whose output terminals are connected in parallel with the output terminals of the rectifier; Fig. 2 shows a battery which may be employed to float on the power circuit and, in conjunction with anti-resonant circuitmeans, to suppress alternating currents which may be impressed upon the system; and Fig. 3 repre sents an arrangement in which a plurality of anti-resonant circuits are interposed between the output of the rectifier of polyphase current and the power circuit in order to suppress certain selected harmonic components which may be troublesome to exposed telephone circuits.

Referring to Fig. l of the drawing, a reference character S designates leads from which alternating current of proper phase and frequency may flow, this current'being derived from a suitable alternator or the like (notshown). Current flowing over leads S energizes the primary of the transformer T. The secondary of transformer T is arranged so as to obtain current of difierent phase from that impressed upon its primary. Thus, the secondary of transformer T may derive six-phase current from, for example, threephase current impressed upon its primary.

A rectifier R is connected to the secondary of transformer T and is employed for rectitying the current it derives. This rectifier may be of any well known type, preferably one exhibiting a low internal impedance. One form of rectifier frequently employed for rectifying six-phase currents is of the mercury arc type. Such a rectifier may include a plurality of anodes A to A inclusive, each anode being connected to a corresponding winding of the secondary of transformer T. The midpoint of the secondary of transformer T is connected to one terminal of a power circuit M. The cathode K of rectifier R is connected to the other terminal of the power circuit through a reactor L In shunt with reactor L there is a variable condenser C The details of the rectifier are not shown or described herein because it is felt that these details are well known to those skilled in the art. The ower circuit M may be terminated by a load 8, receiving the voltage transmitted over this circuit.

The apparatus characteristic of certain features of an embodiment of this invention may be employed in connection with the mercury arc rectifier, as already stated, or with several mercury arc rectifiers connected in any well known manner and with a power line supplied with current from the rectifier or rectifiers, this apparatus necessarily including means for reducing alternating currents superimposed upon the direct current produced by the rectifier.

One form of arrangement for reducing and substantially eliminating the superimposed alternating currents, may include a rotary converter RC, which operates with its output terminals connected to the power circuit M. A rotary converter may be essentially a direct current machine having a direct current armature of ordinary design, the windings of which may be tapped for connection to slip rings and having the ordinary and well known connections to its commutator. The field system may be the same as any direct current machine; it may be shunt or compound wound and excited. Alternating currents are impressed upon its armature and, consequently, direct current voltages are transmitted to its output brushes.

The rotary converter RC has three slip rings SR SR and SR at its alternating current side for connection to the leads S, leading to a source of alternatingcurrent which may generate current of 60 cycles having three phases. The direct current side of the rotary converter includes a pair of output brushes BR and BB which are connected to opposite sides of the power circuit M.

A telephone line N, or any other circuit, may be exposed to the power circuit M. Such a circuit may be very long and may be terminated by telephone substations of any well known type. As is well known, each substation usually includes a telephone receiver having a vibrating diaphragm. Such a vibrating diaphragm may have a resonant period around 1100 cycles, and it may still be in resonance at adjacent frequencies which may extend over a considerable range or band. Any alternating currents which become induced in the telephone circuit may tend to interfere with the quality of the speech transmitted over the telephone circuit.

The rotary converter RC, interposed between the source of alternating current and the power circuit, provides a by-pass for alternating currents superimposed upon the direct current produced by rectifier R. The rotary converter provides a path of low impedance for these alternating current components, whereby the tendency of their presence in the power circuit M is greatly reduced. Accordingly, these alternating current components cannot become induced in the telephone circuit N and cause interference therein.

While the rectifier It causes the rectification of alternating current transmitted thereto, the rotary converter RC performs a similar function, and in addition, in con junction with the series anti-resonant circuit consisting of the inductances L and the condenser C effectively suppresses any alternating current components produced by the rectifier R and which are superimposed upon its direct current output. The rotary con verter RC may supply current to the power circuit M when the load becomes too great, especially if the rectifier R is limited to a certain maximum output.

It will be understood that the rotary converter RE is shown merely schematically and that the details of its construction need not be shown or described in order to understand the principles underlying this invention.

Fig. 2 shows another embodiment of this invention, in which the output terminals P of the rectifier R are connected to the power circuit M through a series anti-resonant circuit consisting of the reactor L and the condenser C a battery B floating on the power circuit M. This battery B may consist of a plurality of cells exhibiting a terminal voltage substantially the same as the voltage of the direct current derived from the rectifier. Battery B may preferably be a wet or storage battery. The positive and negative terminals of the battery B are connected to the corresponding terminals of the power circuit M. Accordingly, the battery floats on the power circuit. When the terminal voltage of the battery B falls below the voltage of the current supplied by the rectifier R, battery B becomes charged, the rate of charge dependingupon the magnitude of the difference between these voltages. lVhen the load becomes greater than normal, the battery B will discharge into the power circuit M and supply the additional current required to maintain the overload condition. Thus, battery B fioa-ts on the power circuit M, becoming charged by current from the rectifier 33 when the load is below the normal value, and discharging into the power circuit M when the load exceeds the normal value.

1 In addition to acting as a floating device upon the power circuit M, the battery B also provides a path of low impedance for alternating currents. Due to the low impedance of the battery B, as compared to the impedance of the series anti-resonant circuit con sisting of the reactor L and the condenser C and the power circuit M, alternating currents become by-passed therethrough. Accordingly, the direct current produced by the rectifier and transmitted over the power circuit M becomes freed from alternating current components. Thus, an exposed circuit, such as N, cannot receive these alternating currents by induction.

It may be stated generally that alternating currents produced by a rectifier, such as a polyphase rectifier of the mercury arc type, are harmonics of a frequency nf, where a represents the number of phases in the current and 7' its frequency. Thus, six-phase, cycle alternating current, when rectified, may have superimposed upon the direct current, component, harmonics having frequencies of 360, 720, 1080, 1440, 1800 cycles, etc. The rotary converter of Fig. 1 and the battery of Fig. 2 are employed in connection with anti-resonant circuits primarily for suppressing these harmonics.

Fig. 3 of the drawing shows an arrangement including two series anti-resonant circuits having windings L and L and condensers C and C respectively. These windings and condensers may be changed in their magnitudes of inductance and capacity, respectively, in order that they may assume any desired resonant periods. Since twelvephase, (SO-cycle alternating current, for example, may have superimposed upon its direct current component, harmonics of a frequency of 720 cycles, these anti-resonant circuits may be tuned to resonance at the frequencies of 720 cycles and 1440 cycles, for example, in order that any exposed circuit, such as a telephone circuit, which may be most sensitive to those frequencies, may become freed from inductive interference. It will be understood that the series anti-resonant circuits need not necessarily be tuned to these harmonics, and that they may be tuned to different harmonics than those mentioned, and that they may be tuned to frequencies different from harmonics of the fundamental frequency, which 'may somehow become superimposed upon the system and may become troublesome by induction to exposed circuits. The power circuit M is shown to be shunted by a device F, which may preferably be any device exhibiting a low impedance.

It will be understood that anyone of the series anti-resonant circuits is effective in suppressing not only current of the frequency of resonance but also currents of frequencies adjacent thereto within a considerable range or band.

The windings in series with the power circuit, such as L; in Figs. 1 and 2, and L and L in Fig. 3, should be designed to carry the full direct current output of the rectifier continuously and to stand momentary overloads. The resistance of these windings should be very small in order that excessive copper losses shall not be introduced into the power system. It will be understood that these windings may be of the iron core type or of the air core type, as found desirable.

It will be obvious that the values assigned to the elements comprising the disclosed embodiments of this invention are given herein merely for the sake of illustration and that any other values may be given to these elements within the scope of the invention.

While this invention has been pointed out in certain particular embodiments merely "for the purpose of illustration, it will be understood that. the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

lVhat is claimed is:

1. The combination of a source of alternating current, a rectifier for rectifying the alternating current, a power circuit to be supplied with the rectified current, a parallel resonant circuit serially interposed between the power circuit and the rectifier, and a r0- tary converter coupling the power circuit with the source of alternating current, the rotary converter acting to by-pass alternating current components superimposed on the directcurrent components of rectification introduced by the rectifier.

2. In a current rectification system adaptable for substantially eliminating alternating current components which may be induced in an exposed telephone circuit, the combination of a source of alternating current, a rectifier for rectifying the alternating cur rent, a power circuit to be supplied with the products of rectification, and a. rotary converter having alternating current inputterminals and direct current output terminals, the input terminals of the rotary converter being coupled to the source of alternating current, the output terminals of the rotary converter being coupled to the power circuit, alternating current components introduced by the rectifier seriously affecting the trans mission over the exposed telephone circuit, the alternating current components being shunted through the output terminals of the rotary converter.

3. In a current rectification system adapted to substantially eliminate alternating current components which may become induced in an exposed telephone circuit, the combina tion of a rectifier connected to a source of q polyphase alternating current, a power circuit to be supplied with the output of the rectifier, a rotating element operated from x the source of polyphase alternating current, said rotating element including a low impedance device shunting the power circuit in order to by-pass alternating current com ponents superimposed on the direct current of the rectifier, and a plurality of antiresonant circuits serially interposed between the rectifier and the power circuit, said antiresonant circuit having resonant periods at selected harmonics of the current rectified by the rectifier which may most likely afi'ect the qualitative transmission over the exposed telephone circuit.

In testimony whereof, I have signed my name to this specification this 16th day of November, 1927.

PAUL W. BLYE. 

